[chuckster57]

Welcome to the forum

Lets try to address the items one thing at a time

Furnace: when you set the thermostat to heat and turn the temp up, the fan starts running. Go outside where the exhaust is and listen for any "clicking", if none then most likely the sail switch has stuck or the igniter is faulty. Having sat for a year and a half, if there wasn't nay screens on the holes paper wasps ( mud dawbers) love to make mud nests on the igniter/burner assembly.

There is an easy way to bench test the furnace, but you have to remove it from the trailer. If your handy I can tell you how to bench test it.

Water heater: the switch at the bottom corner on the outside will allow 120V to the element. The element is located behind that oblong plastic cover. Easy to test for voltage or just make sure the switch is OFF and disconnect the wires. Tet for continuity, if none the element is shot. Takes a 1 1/2" ocket to get it out and then just note the wattage and get another one. There is an O ring to seal it.

water pump: it doesn't run at all? if not then yeah it may have an inline fuse to it, running a water pump without water wont kill it for a few minutes at least. I have run them "dry" for 5 minutes while trying to find them and change the winterizing valve position.